The present invention relates generally to a reactor for depositing an epitaxial layer on a semiconductor wafer, and more specifically to a reactor having a system for equalizing pressure across a gate separating a process chamber of the reactor from a wafer handling chamber.
Conventional horizontal reactors have a process chamber sized and shaped for receiving a semiconductor wafer. When a wafer is loaded, reactant gas is injected into the chamber for depositing an epitaxial layer on the wafer by a process known as chemical vapor deposition. The process chamber is connected to one end of a wafer handling chamber and two load locks are positioned at the other end of the wafer handling chamber so wafers pass through the wafer handling chamber when being transported from the load locks to the process chamber and from the process chamber to the load locks. A port separates the wafer handling chamber from the process chamber and a gate positioned adjacent the port selectively blocks the port to isolate the process chamber during the chemical vapor deposition and unblocks the port to load and unload the wafers.
A conventional Bernoulli wand is sometimes used to transport the wafers between the load locks and the process chamber. The wand includes a horizontally oriented paddle having nozzles directing gas jets generally outward and slightly downward from its lower surface. The gas jets create a vacuum beneath the wand for lifting the wafer without touching it.
The pressures in the process chamber and wafer handling chamber vary with respect to one another throughout the process cycle due to factors such as introduction of purge gas or introduction of gas from the Bernoulli wand. During the wafer loading and unloading steps, the pressure in the process chamber may be different than the pressure in the wafer handling chamber so that when the gate is opened, gas rushes through the port separating the chambers to equalize the pressure in the chambers. Under some circumstances, the pressure differential can cause contaminate laden gas to flow into the chambers through their respective vents. Further, material deposited during previous depositions can be dislodged by gas rushing through the process chamber, the wafer handling chamber and the load locks as pressure is equalized. This dislodged material and other contaminates may settle on wafers, thereby degrading their quality. As a result, it is desirable to equalize the pressure in the process chamber with the pressure in the wafer handling chamber before opening the gate.